Adjustable Rear Iron Sight for a Fire Arm

ABSTRACT

An adjustable iron sight for firearms includes compensation for projectile drop. The projectile drop compensation moves the sight aperture to compensate for projectile drop. Use of the compensation will allow aiming directly at the target without having to visually compensate for projectile drop. The projectile drop compensation mechanism includes a multi-position manually operable wheel and cam that is profiled to match the trajectory of the particular firearm and load. As there are many possible loads that could be used with a particular firearm, the multi-position cam is interchangeable to allow changing to a cam that is matched to the specific load that is desired.

In general, the present invention relates to firearms and particularly, the present invention relates to an adjustable rear iron sight for firearms including height adjustment compensation for projectile drop.

BACKGROUND OF THE INVENTION

Virtually all firearms are equipped with some type of sighting system to facilitate aiming the weapon. Examples of these sighting systems include telescopic sights, holographic sights, laser sights and iron sights. Iron sights also called open sights, consist of a front sight and a rear sight that the shooter aligns together onto the target he/she is aiming at. Iron sights can be either fixed or adjustable and made from iron or any other material

Adjustable iron sights allow for vertical adjustment called elevation and horizontal adjustment called windage. In use the sight is adjusted so that projectiles fired from the firearm will hit the target at the same point that is seen by aligning the sights to the target. This distance from the firearm to the target is known as the zero range. At distances in front of the zero range the projectile will hit the target above the line of sight and at distances beyond the zero range the projectile will hit the target below the line of sight, due of course the projectile drop caused by gravity and changes in velocity.

Typically firearms use an adjustable rear iron sight to compensate for projectile drop and these often use a fine adjustment screw for accurate adjustment. However the fine threads of the vertical adjustment screw often required multiple complete and partial turns to get to the correct setting, with the likelihood of making a mistake in counting that would result in an incorrect setting and also losing the initial zero range setting. Even when the sights have markings these are often difficult to read and generic, that is they require knowledge of the trajectory of the firearm/load combination in order to adjust the single elevation screw to the correct setting.

Some military iron sights from the prior art allow for projectile drop compensation but only for a standardized military load. The increments of elevation are also too large to be useful for hunting.

SUMMARY OF THE INVENTION

It is one object of the invention to provide an improved adjustable rear iron sight for a fire arm.

According to one aspect of the invention there is provided an adjustable rear iron sight for a firearm comprising:

a rear sighting element for mounting at a rear of the fire arm and defining a visible alignment portion for visual alignment by the user with a front sighting element;

a mounting member having mounting elements for attachment of the mounting member to the firearm;

an adjustable member carried on the mounting member and adjustably movable upwardly and downwardly relative thereto;

the sighting element being mounted on the adjustable member so that the upward and downward adjustment acts to change the height of the sighting element on the firearm so as to compensate for projectile drop over different distances;

a manually rotatable wheel mounted on the mounting member for manual rotation by the user about an axis of the wheel;

the wheel carrying a cam for rotation therewith having a generally spiral cam surface defining a spirally changing radius from the axis for engaging an abutment on the adjustable member and moving the adjustable member to a height determined by the radius at any selected position on the spiral cam surface;

the wheel having a plurality of distance markings on a visible surface thereof angularly spaced around the axis for selection by the user of a required distance marking by rotating the wheel to a selected angular position determined by selection of the required distance marking;

the spiral cam surface having a profile of radius changes calibrated such that the distance markings are each associated with a respective required height of the adjustable member.

Preferably there is provided with the mounting member, sighting element and adjustable member a plurality of wheels each having a cam with a different profile of the cam surface where the cam spiral cam surface of each wheel has a profile of radius changes calibrated relative to a different shot load for the fire arm.

Preferably the wheel is readily removable and replaceable for replacement with a second wheel having a cam with a different profile of the cam surface where the cam spiral cam surface of each wheel has a profile of radius changes calibrated relative to a different shot load.

Preferably the wheel is readily removable and replaceable for replacement with a second wheel having a cam with a different profile of the cam surface where the cam spiral cam surface of each wheel has a profile of radius changes calibrated relative to a different fire arm.

Preferably the wheel is attached to the mounting member by a single screw extending along the axis and defining a shaft for rotation of the wheel.

Preferably the rear sighting element is mounted on the adjustable member for side to side movement for adjustment of the rear sighting element to compensate for windage.

Preferably the rear sighting element is mounted on the adjustable member by an adjustment screw.

Preferably the adjustable member is mounted on the mounting member by a pair of upstanding pins allowing sliding movement of the adjustable member on the mounting member.

Preferably the pins carry springs for biasing the adjustable member onto the cam surface.

Preferably the wheel is mounted between the pins below the adjustable member and the springs bias the adjustable member downwardly onto the cam surface.

Preferably the wheel and the mounting member include cooperating elements for restraining the wheel in a plurality of angular positions corresponding to the distance markings on the wheel.

Preferably the cooperating elements comprise series of recesses in one of the mounting member or the wheel and a spring biased ball for engaging into the recesses and carried on the other of the mounting member or the wheel.

Preferably the mounting member comprises an upstanding block with a first upstanding side surface having the mounting elements for attachment of the mounting member to the firearm and a second parallel upstanding side surface carrying the wheel.

According to a second aspect of the invention there is provided an adjustable rear iron sight for use with different firearms having different available shot loads comprising:

a rear sighting element for mounting at a rear of the fire arm and defining a visible alignment portion for visual alignment by the user with a front sighting element;

a mounting member having mounting elements for attachment of the mounting member to the firearm;

an adjustable member carried on the mounting member and adjustably movable upwardly and downwardly relative thereto;

the sighting element being mounted on the adjustable member so that the upward and downward adjustment acts to change the height of the sighting element on the firearm so as to compensate for projectile drop over different distances;

and a plurality of manually rotatable wheels each arranged to be readily removably mounted on the mounting member;

each wheel being arranged, when mounted, for manual rotation by the user about an axis of the wheel;

each wheel carrying a cam for rotation therewith having a generally spiral cam surface defining a spirally changing radius from the axis for engaging an abutment on the adjustable member and moving the adjustable member to a height determined by the radius at any selected position on the spiral cam surface;

each wheel having a plurality of distance markings on a visible surface thereof angularly spaced around the axis for selection by the user of a required distance marking by rotating the wheel to a selected angular position determined by selection of the required distance marking;

each spiral cam surface having a profile of radius changes different from that of the other cam surfaces of the different wheels and calibrated such that the distance markings are each associated with a respective required height of the adjustable member relative to a different shot load for a selected fire arm.

According to a third aspect of the invention there is provided an adjustable rear iron sight for a firearm comprising:

a rear sighting element for mounting at a rear of the fire arm and defining a visible alignment portion for visual alignment by the user with a front sighting element;

an upstanding mounting block with a first upstanding side surface having mounting elements for attachment of the upstanding mounting block to the firearm and a second parallel upstanding side surface;

an adjustable member carried on a top of the upstanding mounting block and adjustably movable upwardly and downwardly relative thereto;

the sighting element being mounted on the adjustable member so that the upward and downward adjustment acts to change the height of the sighting element on the firearm so as to compensate for projectile drop over different distances;

a manually rotatable wheel mounted on the second side surface of the upstanding mounting block for manual rotation by the user about an axis of the wheel extending at right angles to the second side surface;

the wheel carrying a cam for rotation therewith having a generally spiral cam surface defining a spirally changing radius from the axis for engaging an abutment on the adjustable member and moving the adjustable member to a height determined by the radius at any selected position on the spiral cam surface;

the wheel having a plurality of distance markings on a visible surface thereof angularly spaced around the axis for selection by the user of a required distance marking by rotating the wheel to a selected angular position determined by selection of the required distance marking;

the wheel and the mounting member include cooperating elements for restraining the wheel in a plurality of angular positions corresponding to the distance markings on the wheel;

the spiral cam surface having a profile of radius changes calibrated such that the distance markings are each associated with a respective required height of the adjustable member.

The invention also provides a method of adjusting the rear iron sight of a firearm as described above in which the wheel is selected from a plurality of wheels each having a cam with a different profile of the cam surface where the cam spiral cam surface of each wheel has a profile of radius changes calibrated relative to a different shot load for a selected fire arm.

The adjustable rear sight described herein may have one or more of the following features:

allowance to adjust windage and elevation for a zero range;

projectile drop compensation to allow a “dead on” hold at any selected distance;

projectile drop compensation interchangeable to allow using non-standardized loads;

multi-position stops at useful distance intervals;

positive stops to prevent accidental movement;

easy to see markings indicating distance interval;

quick adjustment without needing to use tools.

To attain these features, the arrangement described hereinafter provides a sight mounting block which mounts the sight to said firearm, said sight mounting block containing mounting holes to allow attachment to said firearm, a threaded mounting hole to allow for attaching the projectile drop compensation mechanism, a spring and ball that apply force to maintain the position of the interchangeable multi-position cam and cavities being dimensioned to cooperate with the springs and modified shoulder bolts that control the vertical motion of the aperture mounting block; a projectile drop compensation mechanism which comprises a mounting shoulder screw and an interchangeable multi-position cam that raises the aperture mounting block via the vertical elevation screw, said cam profile to match the trajectory of the particular firearm and load; an aperture mounting block containing threaded holes for fastening the shoulder bolts that control its vertical motion, a vertical elevation screw, a horizontal windage screw, a threaded aperture block and an aperture.

To provide allowance to adjust windage, a horizontal windage screw is contained in the aperture mounting block. Turning the screw clockwise causes the aperture block and aperture to move to the right as a result moving the point of impact to the right and turning the screw counter-clockwise causes the aperture block and aperture to move to the left as a result moving the point of impact to the left

To provide allowance to adjust elevation for the zero range, a vertical elevation screw is contained in the aperture mounting block. The point of the vertical elevation screw rests on the profiled section of the interchangeable multi position cam. With the cam set to its lowest setting, adjusting elevation for the zero range can be performed. Turning the screw clockwise causes the aperture mounting block to raise (containing the aperture block and aperture) as a result moving the point of impact higher. Turning the screw counter-clockwise causes the aperture mounting block to lower (containing the aperture block and aperture) as a result moving the point of impact lower.

Projectile drop compensation is achieved by adjusting the interchangeable multi position cam to the desired distance setting that is the closest match to the distance from the target. The profiled section adds the necessary increase in elevation to the zero range due to its direct contact with the point of the vertical elevation screw. The profile which has been machined into the cam has been determined using ballistic data calculated from customer supplied load information and the spacing between the front and rear sight. If the customer wishes, additional interchangeable multi position cams can be purchased and the customer only needs to install the correct cam to be able to aim “dead on” at any distance selected between the minimum and maximum distance settings.

The front face of the interchangeable multi position cam displays distance settings in large easy to read numbers and lines. The distance intervals are close enough to allow the average point of impact to be will be within 1″ of the zero range at every setting. The circumference is knurled to provide ease of adjustment. Cam position is maintained by pressure of the spring loaded ball located in the sight mounting block engaging depressions in the rear surface of the cam.

Quick adjustments to the desired distance setting are ensured by fact that the sight is always ready to be adjusted. The precision fit of the parts controlling the linear vertical movement prevent any looseness that require additional parts to control in some designs of the prior art. Adjustment to any setting is always less than 1 turn.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will now be described in conjunction with the accompanying drawings in which:

FIG. 1 is a rear elevational view of an apparatus according to the present invention shown mounted to the rear of a fire arm shown is shown schematically only in part cross-section.

FIG. 2 is a side elevational view of the apparatus of FIG. 1.

FIG. 3 is a top plan view of the apparatus of FIG. 1.

FIG. 4 is a rear elevational view along the lines 4-4 of the wheel and cam of the apparatus of FIG. 1.

FIG. 5 is a rear elevational view along the lines 4-4 of the wheel and cam of the apparatus of FIG. 1.

FIG. 6 is an exploded rear view taken in the same direction as FIG. 1 of the apparatus of FIG. 1.

FIG. 7 is an exploded rear view taken in the same direction as FIG. 2 of the apparatus of FIG. 1.

In the drawings like characters of reference indicate corresponding parts in the different figures.

DETAILED DESCRIPTION

An adjustable rear iron sight 10 is provided for a firearm 11 for cooperation with a fixed front sight (not shown) where the user aligns the front and rear sights to aim the fire arm in a required direction.

The sight comprises a rear sighting element 12 which is shown in the form of an aperture 13 carried in a screw-in insert portion 14 for mounting in a housing 15. This is mounted generally at a rear of the fire arm and defines a visible alignment portion defined by the aperture for visual alignment by the user with the front sighting element (not shown). Other types of sighting elements can be used which allow the user to locate the rear sight relative to the front sight as are well known in the industry.

In general, the element 12 is carried on an a mounting member in the form of a mounting block 16 having mounting elements 17 for attachment of the mounting member 16 to the firearm 11. An adjustable member 18 is carried on the mounting member 16 and is adjustably movable upwardly and downwardly relative thereto.

The sighting element 12 is mounted on the adjustable member 18 so that the upward and downward adjustment of the adjustable member 18 acts to change the height of the sighting element 12 on the firearm 11 so as to compensate for projectile drop over different distances.

A manually rotatable wheel 19 is mounted on the mounting member 16 for manual rotation by the user about an axis 20 of the wheel. The wheel 19 carries a snail cam 21 for rotation therewith having a generally spiral snail cam surface 22 defining a spirally changing radius from the axis 20 for engaging an abutment on the adjustable member 16 and moving the adjustable member 16 to a height determined by the radius at any selected position on the spiral cam surface 22.

The wheel 19 has a plurality of distance markings 19A on an outer circular visible surface 19B thereof angularly spaced around the axis 20 for selection by the user of a required distance marking by rotating the wheel to a selected angular position determined by selection of the required distance marking. The markings are shown as 100 to 200 yards but can vary depending on the parameters of the fire are concerned.

The spiral cam surface has a profile of radius changes calibrated such that the distance markings 19A are each associated with a respective required height of the adjustable member and therefore of the sight 12 carried by it.

The wheel 19 is cylindrical with an outer circular surface carrying the markings. A peripheral surface 19C is knurled for finger adjustment. The wheel is readily removable and replaceable for replacement with a second wheel 19D (FIG. 4) having a cam 20 with a different profile 22 of the cam surface where the cam spiral cam surface of that wheel has a profile of radius changes calibrated relative to a different fire arm and/or to a different shot load.

The wheel 19 is attached to the mounting block 16 by a single screw 25 extending along the axis 20 and threaded into the block 16 at female thread 26. The screw 25 defines a cylindrical surface forming a shaft 25A for rotation of the wheel. The block 16 is mounted on the fire arm by pins 17A passing through holes 17 forming the mounting elements. It will be appreciated that the block must be manufactured to accommodate the different mounting pin arrangements required for different fire arms. This mounts the block upstanding along the side of the fire arm with a side surface 16A immediately adjacent the side of the fire arm and an opposed upstanding parallel surface 16B adjacent the wheel 19.

The rear sighting element 12 is mounted on the adjustable member 18 for side to side movement for adjustment of the rear sighting element to compensate for windage. This is effected by providing a thread 12B on the sight 12 to cooperate with a screw 12A mounted across an outwardly projecting portion 18A of the adjustable member 18. The screw 12A is operable by a head not shown for fine screw adjustment across the portion 18A of the sight 12.

The adjustable member includes a main body portion 18B mounted on top of the mounting block by a pair of upstanding pins 28 and 29 allowing vertical sliding movement of the adjustable member 18 along bores 31 and 32 in the mounting block 16 on the pins. The pins are attached by a threaded connection 33A, 33B at the upper end to the main portion 18B of the adjustable member 18. The pins 28, 29 carry springs 34, 35 for biasing the adjustable member onto the cam surface 22 of the cam 20. The springs apply a downward force on shoulders 28A and 29A of the pins relative to shoulders 31A and 32A in the block 16. Downward movement of the portion 18B is limited by an adjustable screw stop 38 in a bore 39 which buts against the top surface of the block 16. The pins 28 and 29 are held in place in the bores 31, 32 by end caps which close the bores and allow the pins to slide though while locating the pin against side to side movement.

The wheel shaft 25A is mounted between the pins 28, 29 below the adjustable member 18 and the springs bias the adjustable member downwardly onto the cam surface so that the cam surface when rotated lifts the adjustable member 18 off the stop 38.

The wheel and the mounting member include cooperating elements 40 for restraining the wheel in a plurality of angular positions corresponding to the distance markings on the wheel. The cooperating elements comprise a series of recesses 40A in the surface 19C of the wheel 19 and a ball 40B biased by a spring 40C for engaging into the recesses 40A. The ball 40B is held in place by a screw 40D engaged into a bore 40E in the block 16.

Thus the upstanding block 16 includes the first upstanding side surface 16A having the mounting pins 17A for attachment of the mounting member to the firearm and the second parallel upstanding side surface 16B immediately adjacent and carrying the wheel 19.

Thus the apparatus includes the sight mounting block 16 which mounts the sight to said firearm 11, said sight mounting block containing mounting holes 17 to allow attachment to said firearm. The spring and ball 40 apply force to maintain the position of the interchangeable multi-position cam 20 and cavities 40A. The block 16 cooperates with the springs 34, 35 and modified shoulder bolts 28, 29 that control the vertical motion of the aperture mounting block 18. The projectile drop compensation mechanism further comprises the mounting shoulder screw 38 and an interchangeable multi-position cam and wheel assembly 19 that raises the aperture mounting block 18 via the vertical elevation screw 38 against which it abuts. The cam profile is arranged to match the trajectory of the particular firearm and load. The aperture mounting block 18 contains threaded holes 39 for fastening the shoulder bolts 28, 29 that control its vertical motion. The sight finally includes the horizontal windage screw 12A, the threaded aperture block 12 and the aperture 13.

To provide allowance to adjust windage, the horizontal windage screw is contained in the aperture mounting block 18. Turning the screw clockwise causes the aperture block and aperture to move to the right as a result moving the point of impact to the right and turning the screw counter-clockwise causes the aperture block and aperture to move to the left as a result moving the point of impact to the left

To provide allowance to adjust elevation for the zero range, the vertical elevation screw 38 is contained in the aperture mounting block 18. The point of the vertical elevation screw 38 rests on the profiled section 22 of the interchangeable multi position cam 20. With the cam 20 set to its lowest setting, adjusting elevation for the zero range can be performed. Turning the screw 38 clockwise causes the aperture mounting block 18 to raise (containing the aperture block and aperture) as a result moving the point of impact higher. Turning the screw counter-clockwise causes the aperture mounting block 18 to lower (containing the aperture block and aperture) as a result moving the point of impact lower.

Projectile drop compensation is achieved by adjusting the interchangeable multi position cam 20 to the desired distance setting that is the closest match to the distance from the target. The profiled section 22 adds the necessary increase in elevation to the zero range due to its direct contact with the point of the vertical elevation screw 38. The profile which has been machined into the cam 20 has been determined using ballistic data calculated from customer supplied load information and the spacing between the front and rear sight. If the customer wishes, additional interchangeable multi position cams can be purchased and the customer only needs to install the correct cam to be able to aim “dead on” at any distance selected between the minimum and maximum distance settings.

The front face 19B of the wheel 19 of the interchangeable multi position cam displays distance settings in large easy to read numbers and lines. The distance intervals are close enough to allow the average point of impact to be will be within 1″ of the zero range at every setting. The circumference is knurled at 19C to provide ease of adjustment. Cam position is maintained by pressure of the spring 40C against the loaded ball 40B located in the sight mounting block engaging the depressions 40A in the rear surface 19C of the wheel 19 of the cam.

Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without department from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense. 

1. An adjustable rear iron sight for a firearm comprising: a rear sighting element for mounting at a rear of the fire arm and defining a visible alignment portion for visual alignment by the user with a front sighting element; a mounting member having mounting elements for attachment of the mounting member to the firearm; an adjustable member carried on the mounting member and adjustably movable upwardly and downwardly relative thereto; the sighting element being mounted on the adjustable member so that the upward and downward adjustment acts to change the height of the sighting element on the firearm so as to compensate for projectile drop over different distances; a manually rotatable wheel mounted on the mounting member for manual rotation by the user about an axis of the wheel; the wheel carrying a cam for rotation therewith having a generally spiral cam surface defining a spirally changing radius from the axis for engaging an abutment on the adjustable member and moving the adjustable member to a height determined by the radius at any selected position on the spiral cam surface; the wheel having a plurality of distance markings on a visible surface thereof angularly spaced around the axis for selection by the user of a required distance marking by rotating the wheel to a selected angular position determined by selection of the required distance marking; the spiral cam surface having a profile of radius changes calibrated such that the distance markings are each associated with a respective required height of the adjustable member.
 2. The adjustable rear iron sight according claim 1 wherein there is provided with the mounting member, sighting element and adjustable member a plurality of wheels each having a cam with a different profile of the cam surface where the cam spiral cam surface of each wheel has a profile of radius changes calibrated relative to a different shot load for the fire arm.
 3. The adjustable rear iron sight according claim 1 wherein the wheel is readily removable and replaceable for replacement with a second wheel having a cam with a different profile of the cam surface where the cam spiral cam surface of each wheel has a profile of radius changes calibrated relative to a different shot load.
 4. The adjustable rear iron sight according claim 1 wherein the wheel is readily removable and replaceable for replacement with a second wheel having a cam with a different profile of the cam surface where the cam spiral cam surface of each wheel has a profile of radius changes calibrated relative to a different fire arm.
 5. The adjustable rear iron sight according claim 1 wherein the wheel is attached to the mounting member by a single screw extending along the axis and defining a shaft for rotation of the wheel.
 6. The adjustable rear iron sight according claim 1 wherein the rear sighting element is mounted on the adjustable member for side to side movement for adjustment of the rear sighting element to compensate for windage.
 7. The adjustable rear iron sight according claim 1 wherein the rear sighting element is mounted on the adjustable member by an adjustment screw.
 8. The adjustable rear iron sight according claim 1 wherein the adjustable member is mounted on the mounting member by a pair of upstanding pins allowing sliding movement of the adjustable member on the mounting member.
 9. The adjustable rear iron sight according claim 8 wherein the pins carry springs for biasing the adjustable member onto the cam surface.
 10. The adjustable rear iron sight according claim 1 wherein the wheel is mounted between the pins below the adjustable member and the springs bias the adjustable member downwardly onto the cam surface.
 11. The adjustable rear iron sight according claim 1 wherein the wheel and the mounting member include cooperating elements for restraining the wheel in a plurality of angular positions corresponding to the distance markings on the wheel.
 12. The adjustable rear iron sight according claim 1 wherein the cooperating elements comprise series of recesses in one of the mounting member or the wheel and a spring biased ball for engaging into the recesses and carried on the other of the mounting member or the wheel.
 13. The adjustable rear iron sight according claim 1 wherein the mounting member comprises an upstanding block with a first upstanding side surface having the mounting elements for attachment of the mounting member to the firearm and a second parallel upstanding side surface carrying the wheel.
 14. An adjustable rear iron sight for use with different firearms having different available shot loads comprising: a rear sighting element for mounting at a rear of the fire arm and defining a visible alignment portion for visual alignment by the user with a front sighting element; a mounting member having mounting elements for attachment of the mounting member to the firearm; an adjustable member carried on the mounting member and adjustably movable upwardly and downwardly relative thereto; the sighting element being mounted on the adjustable member so that the upward and downward adjustment acts to change the height of the sighting element on the firearm so as to compensate for projectile drop over different distances; and a plurality of manually rotatable wheels each arranged to be readily removably mounted on the mounting member; each wheel being arranged, when mounted, for manual rotation by the user about an axis of the wheel; each wheel carrying a cam for rotation therewith having a generally spiral cam surface defining a spirally changing radius from the axis for engaging an abutment on the adjustable member and moving the adjustable member to a height determined by the radius at any selected position on the spiral cam surface; each wheel having a plurality of distance markings on a visible surface thereof angularly spaced around the axis for selection by the user of a required distance marking by rotating the wheel to a selected angular position determined by selection of the required distance marking; each spiral cam surface having a profile of radius changes different from that of the other cam surfaces of the different wheels and calibrated such that the distance markings are each associated with a respective required height of the adjustable member relative to a different shot load for a selected fire arm.
 15. An adjustable rear iron sight for a firearm comprising: a rear sighting element for mounting at a rear of the fire arm and defining a visible alignment portion for visual alignment by the user with a front sighting element; an upstanding mounting block with a first upstanding side surface having mounting elements for attachment of the upstanding mounting block to the firearm and a second parallel upstanding side surface; an adjustable member carried on a top of the upstanding mounting block and adjustably movable upwardly and downwardly relative thereto; the sighting element being mounted on the adjustable member so that the upward and downward adjustment acts to change the height of the sighting element on the firearm so as to compensate for projectile drop over different distances; a manually rotatable wheel mounted on the second side surface of the upstanding mounting block for manual rotation by the user about an axis of the wheel extending at right angles to the second side surface; the wheel carrying a cam for rotation therewith having a generally spiral cam surface defining a spirally changing radius from the axis for engaging an abutment on the adjustable member and moving the adjustable member to a height determined by the radius at any selected position on the spiral cam surface; the wheel having a plurality of distance markings on a visible surface thereof angularly spaced around the axis for selection by the user of a required distance marking by rotating the wheel to a selected angular position determined by selection of the required distance marking; the wheel and the mounting member include cooperating elements for restraining the wheel in a plurality of angular positions corresponding to the distance markings on the wheel; the spiral cam surface having a profile of radius changes calibrated such that the distance markings are each associated with a respective required height of the adjustable member.
 16. The adjustable rear iron sight according claim 15 wherein the wheel is attached to the mounting member by a single screw extending along the axis and defining a shaft for rotation of the wheel.
 17. The adjustable rear iron sight according claim 15 wherein the rear sighting element is mounted on the adjustable member for side to side movement for adjustment of the rear sighting element to compensate for windage.
 18. The adjustable rear iron sight according claim 15 wherein the rear sighting element is mounted on the adjustable member by an adjustment screw.
 19. The adjustable rear iron sight according claim 15 wherein the adjustable member is mounted on the mounting member by a pair of upstanding pins allowing sliding movement of the adjustable member on the mounting member.
 20. The adjustable rear iron sight according claim 19 wherein the pins carry springs for biasing the adjustable member onto the cam surface. 